We propose to use the isolated rat lung, perfused with Krebs bicarbonate solution containing 4.5 percent bovine albumin, to examine the role of the lung in the metabolism of a number of naturally occurring hormones. This will involve a study of the subsequent catabolism, or incorporation into other substances, in the pulmonary tissue. We intend to characterize angiotensin converting enzyme (ACE) in lung and determine the effects of electrolytes and components of the renin-angiotensin system on the activity of ACE by using spectrophotometric methods already in use. In addition, we will examine the way in which the lung extracts phospholipid precursors (methionine, choline, glucose, palmitate) from the perfusate and determine whether this process is modified by steroids. By using solvent extraction and thin layer chromatographic techniques, we will also examine the rate of incorporation of these precursors into phospholipids. In addition, we wish to determine whether the lung is involved in the metabolism of, or possibly acts as a target organ for, aldosterone and cortisone. Our previous studies have, by an appreciation of the plasma half-life values and by the process of elimination, lead us to suspect that the lung may be involved in the catabolism of the larger peptides. Therefore, we propose to examine the effect of pulmonary perfusion on the activity of prolactin, relaxin, gastrin, luteinising hormone and follicle stimulating hormone, using radioimmunoassay techniques currently in use in our laboratory. Finally, we propose to examine the role of other naturally occurring hormones (angiotensin II, vasopressin, insulin, glucagon, deoxycorticosterone, cortisone) on the uptake of norepinephrine and serotonin, which we have already characterized and on the uptake of PGF 2 alpha, for which we already have an immunoassay.